Using the fractional calculus approach, we present the Laplace analysis of an equivalent electrical circuit for a multilayered system, which includes distributed elements of the Cole model type. The ...Bode graphs are obtained from the numerical simulation of the corresponding transfer functions using arbitrary electrical parameters in order to illustrate the methodology. A numerical Laplace transform is used with respect to the simulation of the fractional differential equations. From the results shown in the analysis, we obtain the formula for the equivalent electrical circuit of a simple spectrum, such as that generated by a real sample of blood tissue, and the corresponding Nyquist diagrams. In addition to maintaining consistency in adjusted electrical parameters, the advantage of using fractional differential equations in the study of the impedance spectra is made clear in the analysis used to determine a compact formula for the equivalent electrical circuit, which includes the Cole model and a simple RC model as special cases.
Through the structural optimisation, the Halbach array-linear vernier permanent magnet machine (H-LVPMM) offers a higher force with extremely low ripple. However, thrust force ripple is minimised ...rather than eliminated and it reduces the precision of the control system. The thrust force ripple includes cogging force, end force and electromagnetic thrust ripple. Since the structural optimisation makes three phases balanced, the electromagnetic thrust ripple can be ignored. Here, a disturbance observer is proposed to observe and compensate the thrust force ripple by injecting the correspondent harmonic current into the closed-loop controller in a feedforward method. It leads to second, fourth and sixth harmonic components in the q-axis current. The closed-loop current control with vector proportional and integral (VPI) regulator is applied to guarantee the current tracking accuracy of the harmonic components. Parameters are optimised according to the thrust force ripple harmonics and the open-loop Bode diagram. The impact of thrust ripple is eliminated by the proposed control method. Experimental results show the validity of the disturbance observer and the VPI current controller.
A three‐phase interleaved high step‐up bidirectional DC–DC converter is proposed, which can achieve three times the voltage gain of the traditional three‐phase interleaved boost converter only by ...adding two capacitors. The proposed converter has the characteristics of low switch voltage and current stresses, low output voltage ripple, automatic voltage‐balancing and current‐sharing abilities. Compared with the traditional interleaved switching strategy, a 180° interleaved switching strategy is proposed, which is more suitable for the proposed converter by widening the working duty cycle range. Closed dual‐loop control is used to regulate the output voltage of the converter. The parameter determining the method of the closed‐loop controllers based on the Bode diagram is described in order to control the high‐order converter. Operating principle, modelling, steady‐state analysis, voltage‐balancing and current‐sharing ability analysis and closed‐loop design of the converter are studied in more detail. Finally, experimental verification and efficiency measurements are implemented by a 300 W, 24 V input to 230 V DC bus prototype, which proved that the proposed converter is more suitable than the traditional three‐phase interleaved boost converter for some applications where requiring about six to ten times the voltage conversion ratio.
This study presents a procedure for tuning proportional–integral/proportional–integral-derivative controllers using the frequency response method via Bode diagrams, which is relatively simple and ...easy to understand, and can be used when phase margin and 0 dB gain crossover frequency are project specifications. The method is validated in a practical power electronics application, considering the current and the DC-bus voltage loops of a shunt active power filter (SAPF). A detailed analysis related to the obtaining of the DC-bus voltage loop is also provided. In addition, a stability analysis is presented, considering how the SAPF compensation current is influenced according to the load current, taking into account different values of the grid impedance. Simulation and practical results show the effectiveness of the proposed scheme and its simplicity for being considered in practical cases.
The main standard for avionic equipment DO-160G defines a set of tests that require compliance before the employment of a device in aircraft. An important test involves the generator voltage and ...consequential current distortion of the three-phase load in the variable 360-800 Hz frequency grid. The main purpose of this paper is to present and analyze a systematic design methodology for three-phase boost and buck rectifiers in order to meet with the voltage distortion test requirement. For a given voltage harmonic profile, the current harmonic limits that have to be satisfied are translated into equivalent per-harmonic admittances and a profile of maximum rectifier input admittance versus frequency is obtained. The defined profile, due to normalization, is applicable to arbitrary power level with simple shifting by the base admittance governed by the converter nominal power. It is shown that for boost-type rectifiers there is a tradeoff between current controller bandwidth and input inductor size, while for the buck-type rectifiers main limitation lies in the input LC filter design used for differential electromagnetic interference filtering. The experimental results conducted on an SiC three-phase 10 kW VIENNA rectifier are tightly backing up the proposed theoretical analysis. This paper is accompanied by three videos demonstrating experimental measurement of d-axis open-loop duty cycle to inductor current transfer function, loop-gain of d-axis current controller with 3.8 kHz bandwidth and variable grid frequency 360-800 Hz operation of the converter under 0% and 10% input three-phase voltage total harmonic distortion.
Resonant converters are often studied using their envelope models (EMs), i.e., the transfer functions (TFs) that relate the envelope of the output quantities to those of the input ones. TFs can ...accurately represent only the input-output relations of linear systems and hence any method used to develop the EM cannot be accurate if the resonant converters process the envelopes in a nonlinear way. This article works out a general criterion that recognizes whether the envelope processing is linear or not, the type of the eventual non-linearity and its amount. The criterion is expressed in terms of conditions that have to be fulfilled by the input-output Bode diagram of the converter. These conditions are of general validity and do not depend on the converter topology; their applicability is not limited to resonant converters, but it can be extended to any system. The conditions have been derived by reviewing the procedure that leads to the modulated variables Laplace transform method for the development of the EMs. The theoretical results are verified at first by simulations and then by experimental tests carried out on two different resonant topologies of a prototypal converter that works as wireless battery charger.
In addition to their conventional use in electric motor drives, DC-DC converters have a variety of other uses, such as energy storage, energy conversion, cyber security systems, uninterruptible power ...supplies, and renewable energy systems. An innovative DC-DC converter is suggested in this article. Designing a new, high-gain DC-DC converter scheme known as a double-switch SEPIC-buck converter (DSSB) is possible after making some adjustments to the SEPIC converter that is currently known in accordance with accepted techniques. The output voltage magnitude of the proposed converter is either larger than or less than the input voltage magnitude and is the same sign as the input voltage. According to the theoretical and analytical study that has been supported by the real-world application, high voltage gain, low switching stress, and low inductor current ripple are the main characteristics of the proposed DSSB converter. The related small-signal model was also used to build the closed-loop system. The frequency response and output voltage behavior were investigated when the input source voltage abruptly changed as a step function. Based on the comparison study with other DC-DC converters, the DSSB converter outperforms currently known DC-DC converters such as Buck, SEPIC, Boost, Buck-Boost, and other SEPIC converter topologies in terms of voltage gain, harmonic content, normalized current ripple, dynamic performance, and efficiency. Additionally, the frequency response and control of the proposed converter using an alternate current (AC), small-signal, analysis-based, current-mode control technique are both provided. Thus, the DSSB is regarded as safe in overcurrent situations because of the small-signal analysis with the current control strategy. As a result of the verification of the proposed control technique, the resistance to changes in the DSSB parameters, improved dynamic performance, and higher control accuracy are further advantages of current-mode control based on small-signal analysis over other control approaches (PI controllers). Finally, the experimental and simulation results from Simplorer 7 and MATLAB/Simulink are used to validate the findings of the analytical and comparative investigation.
Composites of mesoporous silica SBA-15 and MgO/KCl were prepared by a simple grind method following a heat-treatment process. Their structures were characterized by X-ray diffraction (XRD). Humidity ...sensing properties were studied and the results indicated that, under the same preparation condition, KCl–SBA-15 composite was more suitable to be a promising humidity sensing material than MgO–SBA-15 composite. The impedance of KCl–SBA-15 composite changed more than four orders of magnitude when relative humidity changed from 11% to 95%. The response and recovery time were about 6s and 26s, respectively. High stability and low hysteresis were also observed. Complex impedance spectra, the corresponding equivalent circuit, and bode diagrams under different relative humidity was analyzed to explore the humidity sensing mechanism of this material.
•Alternative method to detect errors in EIS spectra.•Overcome of some practical issues for assessment of simple spectra.•Elucidation of analytical correlations between magnitude and phase.
New ...analytical correlations between impedance magnitude and phase are developed and presented. These correlations are used for the assessment of impedance spectroscopy data. As correlations are obtained, they can be calculated point to point at each frequency of the spectra with no need to establish explicit premises related to stability, linearity or finite limits for their derivation. Their use is simpler than that based on the direct evaluation of the Kramers-Kroning transforms or alternative methods. An example of their derivation from basic equations involving complex numbers is described. They were obtained by looking for an explanation of the empirical fact that the slope of the Bode-Magnitude diagram vs frequency resembles the shape of the corresponding Bode-Phase diagram. Unlike the Kramers-Kronig transform, these new correlations can also be directly applied to test spectra with highly predominant capacitive or inductive responses or even incomplete loops. Their analytical expressions are exact for simple ideal elements and circuits, including the Warburg diffusion element. These correlations were tested with simulated spectra altered with known random error distributions, and they were able to detect the random distribution and the error level for simple spectra when the errors were > 0.5%. For more sophisticated spectra, the minimum error that can be detected without interference of the deviations due to the proper algorithm are around 2.5%. No exact correlation was found for a constant phase element (CPE), but a close empirical approximation was obtained for a single CPE. It is necessary to improve this approximation when a CPE is combined with some other elements because of detected deviations. In addition, it was found that in a first approach the algorithm does not detect non-linear behavior on a simple experimental circuit, but the test gave insights of how to detect it. On the contrary, it is well suited for detection of system stability issues. Examples of their application to actual experimental spectra, high capacitive or with several loops, are presented and the limitations discussed. More work and exhaustive tests are necessary to improve the method and stablish its real limitations, but its use for assessment of simple spectra at certain error level can already be done. Given that the derivation of the new correlations is only based on its complex number nature, this study concludes that the magnitude and phase of any complex number or 2D vector are not independent, and it is expected that similar correlations can be applied to any frequency-dependent complex variable, vector or transfer function, such as those used in optics or rheology.
This paper is focused on the modeling and simulation of a hysteresis current-mode regulated high-gain DC–DC converter intended for solar applications. First, the study effort outlined the working ...principle of a novel high-gain DC–DC converter scheme called a double-switch SEPIC-buck converter (DSSB). This work also presents the dual hysteresis current control technique, which aims to enhance the system's performance and lower the harmonic content of its voltages and currents. Two dual hysteresis current controllers independently control the source and load currents of the proposed converter. The frequency and hysteresis bandwidth are also simultaneously set using the two controllers. Compared to other standard DC–DC converters (buck, SEPIC, boost, and buck-boost), DSSB has better efficiency, a larger voltage gain, and superior dynamic characteristics. The suggested topology has a peak efficiency of 95% and a voltage gain of 1+DD/1-D. The suggested DSSB converter has a THD of 6.6% and an efficiency of 97–98% when compared to various DC–DC converters, while the conventional SEPIC converter, along with boost, buck, and buck-boost converters, have a THD of 10% and an efficiency of 95–97%. Additionally, the DSSB converter has a far smaller crest factor than all other DC–DC converters, including boost, buck, buck-boost, and SEPIC. The suggested converter's performance is theoretically assessed using simulations based on Matlab/Simulink software under various circumstances. The results of simulation work in Matlab/Simulink corroborate the findings of the analysis and investigation.
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